The present invention relates to a composition for molding a biodegradable plastic, a biodegradable plastic product from the composition, and particularly to a biodegradable sheet and a method of the production thereof, and use of the biodegradable sheet
In recent years, biodegradable plastics have considerable attention, which have functions similar to those of general plastics during its use, and which are degraded into compounds each having a relatively low molecular weight, and are finally decomosed into gaseous carbon dioxide and water due to the functions of microorganism existing in the natural kingdom; thus, various kinds of biodegradable plastics have been developed.
Such biodegradable plastics are roughly classified into microorganism product type plastics obtained from aliphatic polyesters produced by microorganisms; plastics originated from natural macromolecules such as starches and cellulose acetates (see, for example, Japanese Patent Laid open publication Nos. H3-24101, H3-31333, H4-500834, H4-501136, and H8-59892); and plastics produced from chemically synthetic raw materials including polylactic acid (polylactate), polypcyrensaxenate, and polycaproracton etc (see, for example, Japanese Patent Laid open publication No. H9-31176).
Specifically, as described in Japanese Patent Laid open publication Nos. H3-24101, H3-31333, H4-500834, H4-501136, and H8 -59892, raw materials for biodegradable plastics have been known comprising 45% by weight of destructured starch, which is a naturally originating macromolecular material, 15% by weight of pure glycerol, 20% by weight of low density polyethylene, 15% by weight of an ethylene-acrylic acid (acrylate) copolymer, 5% by weight of calcium carbonate, and the like for the production of biodegradable plastics.
Such raw materials are formed, for example, into a film, which is then used in a garbage baggage. In the formation of the biodegradable plastic into a sheet, any of a T-die method, a calendaring method and an inflation method has been used as a rule.
The T-die method is a method suitable for the formation of a sheet having a wide variety of thickness from a thin sheet to a thick sheet in a large scale, whilst the calendaring method is a method suitable for producing a large amount of a thin sheet. The calendaring process is suitable for producing a wide variety of sheets having a various thickness from a thin sheet to a thick sheet in a small amount.
Consequently, any of the methods is selected depending upon the objects and applications of the final product and the number of the product to be produced.
However, the conventional biodegradable plastics have be of the following problems: In producing a sheet utilizing any of the conventional biodegradable plastics, such as the naturally occurring macromolecular, microorganisms originating, or chemically synthesized biodegradable plastics, with a conventional inflation film forming installation, it is difficult to produce a sheet in a stable manner because of the problems associated with the material itself and with the film for ability during the course of melting the material. Even if the conventional calendaring apparatus is used, due to decrease in the viscosity during the course of melting the material and poor separation from rolls, it is difficult to be formed into a sheet having a desired thickness In the T-die method, due to a narrow temperature range for the film forming, it is difficult to be formed into a sheet having a given thickness in a stable manner.
If the biodegradable plastics can be formed into a sheet having a desired thickness, the application of the biodegradable plastics can be proven to extend much more.
Also, the development of a biodegradable plastic has been strongly desired, which is applicable to all of the film forming methods.
An object of the present invention is, therefore, to provide a composition for molding a biodegradable plastic, which is applicable to all of the T-die method, calendaring method, inflation method and the like to provide a suitable biodegradable plastic product, particularly a biodegradable plastic sheet.
Another object of the present Invention is to provide a method for producing a biodegradable plastic product obtained from the composition for molding a biodegradable plastic just mentioned.
Still another object of the present invention is to provide novel applications of the biodegradable sheet.
We have made serious studies and investigation to discover that these objects can be attained if a blend of biodegradable components each having different characteristics is used. As a result, the present invention has been accomplished.
The present invention concerns a composition for molding a biodegradable plastic comprising:
A) a biodegradable component comprising an aliphatic polyester as a main ingredient; and
B) a biodegradable component comprising a starch material containing a destructured starch as a main ingredient.
In the composition for molding a biodegradable plastic, the content of biodegradable component (B) is preferably from 5 to 55 parts by weight based on 100 parts by weight of biodegradable component (A).
Furthermore, in the composition for molding a biodegradable plastic, biodegradable component (B) preferably comprises from 45 to 55% by weight of the biodegradable components, from 12 to 15% by weight of a plasticizer having a high boiling point as an additive and from 1 to 3% by weight of a stabilizer as an additive, and the rest of ethylene-vinyl alcohol copolymer.
Moreover, biodegradable component (A) is preferably an aliphatic polyester represented by the formula: 
wherein m and are independently an integer.
In addition, the composition for molding a biodegradable plastic may contain a biodegradable pigment as an additive.
The present invention is also relates to a biodegradable molded product obtained by forming the composition for molding a biodegradable plastic just mentioned, a biodegradable sheet obtained by forming the composition for molding a biodegradable plastic just mentioned into a sheet.
The biodegradable sheet preferably has a thickness of from 0.05 to 1 mm.
Also, the biodegradable sheet can be formed into a cover product through second or multi-step forming including cutting and conjunction step.
Moreover, the biodegradable sheet can be configured to be an advertisement display body by providing an adhesive layer on one layer, providing an advertisement display portion on another layer, and having through holes provided on the whole surface of the sheet. In this case, the advertisement display body is preferably adhered on a mobile vehicle having windows at the adhesive layer side.